This project seeks to understand the molecular biology of learning and memory in a model system, Drosophila melanogaster, that is known for its well characterized genetics. Preliminary results suggest that the plc21 gene (which encodes phospholipase C) is identical to the mushroom bodies miniature (mbm) gene, mutations which result in structural defects in brain and loss of associative learning. If true, this would suggest that phospholipase C, as a pivotal player in inositol phosphate signaling, is involved in brain structural plasticity and memory. The goal of this project is test the hypothesis that the plc21 gene is identical to the mbm gene. To accomplish this goal, two alternative approaches are proposed: (i) Determine whether the mbm mutation can be rescued by transforming the cloned plc21 gene into the germline; and (ii) Determine whether loss-of-function plc21 mutants exhibit a mbm mutant phenotype. Inasmuch as the neuronal processes in this model system are similar, if not identical, to neuronal processes in humans, the results will be valuable for understanding the biochemistry and molecular biology of mammalian brain and, ultimately, the treatment of mental defects.